Method distinguishing line of sight (LOS) from non-line of sight (NLOS) in CDMA mobile communication system

ABSTRACT

The invention discloses a method that identifies whether a channel is LOS or NLOS in a mobile communication system. After coherent accumulation and non-coherent accumulation have been made by the system, first the method takes power difference between the direct path and the non-direct path in a same power delay profile to identify a channel; and then the result is further determined by {overscore (τ)}/σ difference of a LOS channel and a NLOS channel (where {overscore (τ)} and σ is the mean delay and the RMS delay spread of a multipath power profile, respectively). A channel is determined as a LOS channel, if the power ratio of the Maximum Path to the Local Maximum Path is greater than a threshold K, and simultaneously the arrival time difference between the First Path and said Maximum Path is less than a time interval T; otherwise it is a NLOS channel. The method is easier to implement and compatible with the present mobile communication system.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a National Stage of International Application No.PCT/CN02/00220, filed Mar. 29, 2002 and published in Chinese on Jul. 10,2003 as WO 03/056849 A1. This application claims the benefit of ChineseApplication No. 01145113.0, filed Dec. 30, 2001. The disclosure(s) ofthe above applications are incorporated herein by reference.

FIELD OF THE TECHNOLOGY

The invention generally relates to mobile communication technology,especially to a method that identifies whether a channel is a Line OfSight (LOS) channel or a Non-Line Of Sight (NLOS) channel for a mobilestation location in third generation cellular mobile communicationsystem.

BACKGROUND OF THE INVENTION

In a Code Division Multiple Access (CDMA) mobile communication system,an important way to raise the estimation accuracy of mobile stationlocation is to identify whether the channel is a LOS channel or a NLOSchannel, since the delay estimation error caused by a NLOS channel isthe most serious one of those factors that affect the estimationaccuracy of a mobile station location. The LOS channel can be understoodas the transmitter is line of sight with the receiver, and the NLOSchannel can be understood as the transmitter is non-line of sight withthe receiver.

M. P. Wylie first proposes technique that identifies a NLOS used formobile station location in the article named “The Non-Line of SightProblem in Mobile Location Estimation” [1]. In Sep. 9^(th), 1997, heproposes a patent (with number: U.S. Pat. No. 5,974,329) to the USPTOnamed “Method and System for Mobile Location Estimation” [2], which aimsat the NLOS error correction in the mobile location estimation and takesthe NLOS identifying technique as a main element of the invention. Inhis invention the main thinking to identify a NLOS is as follow.

(1) Make long time recorders for distance between a UE (User Equipment)and a base station measured in every base station;

(2) Make smooth processing for the amount of recorded data;

(3) Identify a NLOS with the fact that the variance measured in a NLOS(after smooth processing, it is caused by geomorphology feature) is muchgreater than the variance measured in a LOS (caused by systemmeasurement error).

The NLOS identifying method proposed by [1] and [2] need to use the timecorrelation properties of a mobile station, i.e., the method is suitablefor identifying LOS channel of a mobile station in a moving state, butit is unsuitable for identifying a LOS channel of a mobile station in astatic state; furthermore, the method need to accumulate data for alonger period of time, which will cause a longer delay and is difficultto satisfy response time requirement of the FCC.

A patent (number CN 01105808.0) named “Method and Device for Identifyinga NLOS channel in a CDMA cellular communication system” [3] has beenapplied by the applicant; in this patent, a LOS identifying method isproposed, which synthetically uses channel loss and multipath powerprofile to identify a LOS channel.

Although the method in [3] has overcome the disadvantage of the methodin [1] and [2] which only identify the LOS at the moving state of amobile station, but in [3], the method has not used the power differencebetween paths, and, the ratio of the mean delay and delay spread{overscore (τ)}/σ in a same power delay profile to identify a LOS, alsothe selected characteristic parameters are not simple and clear enough,so the implementation is relatively complex.

In the article: “ Characterization of UHF multipath radio channels infactory buildings” [4] written by T. S. Rappaport, IEEE transaction onantenna and propagation, vol.37, no.8, pp.1058–1069, August, 1989, basedon the indoor measured data, {overscore (τ)}/σ difference between LOSchannel and NLOS channel at an indoor environment has been discussed,i.e., regularity of multipath power profile in LOS channel and NLOSchannel at the indoor environment has been discussed; the conclusion isthat less {overscore (τ)}/σ shows that energy is concentrated on thefirst path and larger {overscore (τ)}/σ shows that energy isconcentrated on the middle and trail part of the power delay profile. Inreference [4], the discussion about {overscore (τ)}/σ is based on thatthe LOS distance is known and thereby the arriving time of LOS path canbe computed; but in real the detected first path may not be the LOS pathand also how to compute and use regularity of {overscore (τ)}/σ has notbeen discussed there.

SUMMARY OF THE INVENTION

Objective of the invention is to design a method to identify a LOSchannel in a CDMA mobile communication system. With this method based onmultipath searching (including de-spread, coherent accumulation andnon-coherent accumulation), it can be identified that a channel iswhether a LOS channel or a NLOS channel.

One purpose of the invention is to provide a method to identify whethera channel is a LOS channel or NLOS channel according to the powerdifference between a direct path and a non-direct path on the same powerdelay profile.

Another purpose of the invention is to provide a method to furtheridentify whether a channel is a LOS channel or a NLOS channel by meansof {overscore (τ)}/σ difference between a LOS channel and a NLOS channel(wherein {overscore (τ)} is a mean delay of a multipath power profile,and σ is a root-mean-square (RMS) delay spread of the multipath powerprofile), based on the result of above method.

A method for identifying whether a channel is a LOS channel or a NLOSchannel in a mobile communication system, comprises:

A. reading in a power delay profile;

B. selecting a path with maximum power amplitude, i.e. a Maximum Path,from the power delay profile;

C. estimating an average noise power and arrival time of a First Pathand the Maximum Path;

D. detecting a Local Maximum Path value within a searching window, anddetecting whether a power ratio of the Maximum Path to the Local MaximumPath is greater than a threshold K;

E. detecting whether an arrival time difference between the First Pathand the Maximum Path is less than a time interval T;

F. if the power ratio of the Maximum Path to the Local Maximum Path isgreater than the threshold K, and simultaneously the arrival timedifference between the First Path and the Maximum Path is less than thetime interval T, determining the channel being a LOS channel; otherwisedetermining the channel being a NLOS channel.

After the step F, further comprises a step of detecting whether the NLOSchannel determined by Step F is a LOS channel or a NLOS channel, by{overscore (τ)}/σ difference of the power delay profile between the LOSchannel and the NLOS channel, which comprises:

G. computing τ_(i) that is an arrival time difference between a i^(th)detectable path and first detectable path;

H. according to following formulas, computing mean delay {overscore (τ)}and root-mean-square delay spread σ,

${\overset{\_}{\tau} = {{\frac{\sum\limits_{i = 1}^{n}{\tau_{i}*p_{i}}}{\sum\limits_{i = 1}^{n}p_{i}}\mspace{31mu}{\overset{\_}{\tau}}^{2}} = {{\frac{\sum\limits_{i = 1}^{n}{\left( \tau_{i} \right)^{2}*p_{i}}}{\sum\limits_{i = 1}^{n}p_{i}}\mspace{31mu}\sigma} = \sqrt{{\overset{\_}{\tau}}^{2} - \left( \overset{\_}{\tau} \right)^{2}}}}};$

I. computing {overscore (τ)}/94 that is a ratio of mean delay toroot-mean-square delay spread of power delay profile; if {overscore(τ)}/σ is less than Delta(Δ), determining the channel being a LOSchannel, and if {overscore (τ)}/σ is not less than Delta (Δ),determining the channel being a NLOS channel;

wherein {overscore (τ)} is a mean delay of a power delay profile and σis a root-mean-square time-delay spread of the power delay profile;wherein n is number of detectable paths, p_(i) is the i^(th) path power,and i is 1 to n.

Wherein the Delta is taken between 0.5 to 1.

Wherein Step D further comprises, if there is no detectable path in thesearching window of the Local Maximum Path, taking Theta (θ) multiplesof the average noise power as the Local Maximum Path power.

Wherein the Theta (θ) is taken 2.

In Step D, the said Local Maximum Path is selected from a range withinAlpha (α) microsecond that delays the Maximum Path; the Alpha (α) widthis greater than one chip.

In Step D, the threshold K in indoor environment, is set less than thethreshold in outdoor environment, and the threshold in outdoorenvironment is set 10.

Wherein Step D further comprises, dividing the threshold K into K1 andK2, wherein K1>K2;

wherein Step F further comprises, if the power ratio of the Maximum Pathto the Local Maximum Path is greater than K1, determining the channel asa LOS channel; if the ratio is less than K2, determining that thechannel is a NLOS channel; and if said ratio is between K1 and K2,determining that the channel is an undetermined channel.

The threshold K1 is taken 10 and K2 is taken 5.

The time interval T is within three chips, and typically two chips.

Comparing with the technical scheme in [3], the technical scheme of theinvention uses the power difference between paths on the same powerdelay profile, and uses {overscore (τ)}/σ to identify a LOS channel({overscore (τ)} is the mean delay and σ is the RMS delay spread of themultipath power profile).

A special feature of the invention is that the method for identifying aLOS channel can be used to a mobile station (terminal) either in amoving state or in a static state. Implementation of the method deploysthe present signal processing techniques for a communication system,such as de-spread, coherent accumulation and non-coherent accumulationetc., so implementation is simple and compatible with various mobilecommunication systems.

Simulation shows that the method which uses the power difference betweena direct path and a non-direct path on same power delay profile caneffectively differentiate a LOS channel or a NLOS channel, but also themethod which uses {overscore (τ)}/σ difference between a LOS channel anda NLOS channel and is based on the result of above method caneffectively differentiate a LOS channel or a NLOS channel. When theabove methods are involved in the location estimation algorithm, themobile station positioning accuracy is obviously increased.

The method for identifying a LOS channel may also be used to identify achannel in high speed data transmission.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows diagrams of power difference between a LOS path and a NLOSpath on a same power delay profile; wherein FIG. 1 a is typical powerdelay profile of a LOS channel, and FIG. 1 b is typical power delayprofile of a NLOS channel.

FIG. 2 shows diagrams of {overscore (τ)}/σ difference between a LOSchannel and a NLOS channel; wherein FIG. 2 a is the curve obtained bytaking theoretical arrival time of a LOS path as the reference point,and FIG. 2 b is the curve obtained by taking arrival time of themeasured First Path as the reference point.

FIG. 3 shows a flowchart to determinate the LOS/NLOS channel based onpower difference between specific paths.

FIG. 4 shows a flowchart to identify a NLOS channel synthetically usingpower difference between paths and {overscore (τ)}/σ.

FIG. 5 shows a system diagram of an embodiment of the invention which isused to identify a LOS channel.

EMBODIMENTS OF THE INVENTION

The invention will be described in more detail with reference to thedrawings.

FIG. 1 shows the power difference of a LOS path and a NLOS path on asame power delay profile. The abscissa is the relative delay withmicrosecond as a unit; the ordinate is the power with dB as a unit. InFIG. 1, the First_Path is the first path, the Max_Path is the maximumpower amplitude path and the Second_Max_Path is the second poweramplitude path; the Alpha (α) is an interval width and theLocal_Max_Path is the local maximum power amplitude path; the searchingwindow for the Local_Max_Path is from the starting point to the endingpoint.

FIG. 1 a is a typical power delay profile of a LOS channel after havingbeen processed with coherent accumulation and non-coherent accumulation;FIG. 1 b is a typical power delay profile of a NLOS channel after havingbeen processed with coherent accumulation and non-coherent accumulation.

As shown in FIG. 1 a, the characteristics of a LOS channel power delayprofile are: at the beginning location or 1 to 2 chips delay of powerdelay profile, there is a strongest path (Max_Path) of which strength isRicean-distributed; within interval Alpha (α) that directly followsbehind the strongest path, there are quasi-LOS paths caused by strongreflection of terrain, and amplitudes of them have no great differencewith the amplitude of the strongest path but they are attenuatedrapidly; after Alpha (α), there are typical NLOS paths and the strengthof them is Rayleigh-distributed, and the Local_Max_Path is searched inthe searching window (from the starting point to the ending point).Measurement shows the Local_Max_Path amplitude (−30 dB in FIG. 1 a) isobviously lower than the Max_Path amplitude (0 dB in FIG. 1 a), and ingeneral the Local_Max_Path amplitude is lower than the Max_Pathamplitude more than 10 dB (it is 30 dB in FIG. 1 a). The difference ofthese two amplitudes is a base to identify a LOS channel in thisinvention.

As shown in FIG. 1 b, the characteristics of a NLOS channel power delayprofile are: at the beginning location or 1 to 2 chips delay of it,there is the first path First_Path, then the strongest path Max_Path,and then an Alpha (α) interval; after the Alpha (α) interval they are atypical NLOS paths and the Local_Max_Path is searched in this searchingwindow (from the starting point to the ending point as shown in FIG. 1b). Measurement shows that there is no obviously difference between theamplitude of the Local_Max_Path and the amplitude of the Max_Path; thisfeature is a base to identify a NLOS channel in this invention.

FIG. 2 shows the {overscore (τ)}/σ difference of the power delay profilefor a LOS channel and a NLOS channel (wherein {overscore (τ)} is a meandelay of a multipath power profile, and σ is a root-mean-square (RMS)delay spread of the multipath power profile). In FIG. 2, the abscissa isa sample sequence number of the power delay spread, i.e. the power delayspread sequence number; and the ordinate is the ratio of {overscore(τ)}/σ, i.e. a mean delay/a RMS time-delay spread.

FIG. 2 a takes the arriving time of the LOS path as the starting pointto compute the values of {overscore (τ)}/σ curve for LOS channel andNLOS channel. It is seen that the average value of {overscore (τ)}/94for the LOS channel is about 0.65 under the threshold (it is 1.0 asshown in FIG. 2), and the average value of {overscore (τ)}/σ for theNLOS channel is about 1.5 above the threshold; so taking {overscore(τ)}/σ=1 as a threshold, it is easier to differentiate the two kinds ofchannels.

FIG. 2 b takes the first path having been measured as the starting pointto compute the values of {overscore (τ)}/σ curves for LOS channel andNLOS channel; the real-line shows the {overscore (τ)}/σ curve of the LOSchannel, and the dot-line shows the {overscore (τ)}/σ curve of the NLOSchannel. Comparing FIG. 2 a and FIG. 2 b, it is shown that for the LOSchannel the average value in FIG. 2 b is decreased a little than in FIG.2 a (it is 0.65 or so), but for the NLOS channel the average value inFIG. 2 b is obviously decreased than in FIG. 2 a (it is decreased from1.5 to 1.0, decreasing about 0.5).

FIG. 2 b shows that, there is an ambiguous zone for {overscore (τ)}/σcurve of the LOS channel and {overscore (τ)}/σ curve of the NLOSchannel, but when the {overscore (τ)}/σ value is less than a specificvalue (it is 0.65 in FIG. 2 b), it is determined that the channel is aLOS channel. This is the base of the invention to use {overscore (τ)}/σvalue for further identifying a LOS channel after having been identifiedby the amplitude difference between different paths.

FIG. 3 shows a basic flowchart to identify a LOS channel or a NLOSchannel by using power strength (amplitude) difference between a directpath and a non-direct path.

In the first step, read in the power delay profile and extract itscharacteristic parameters; said power delay profile is obtained afterthe system has performed the coherent accumulation and non-coherentaccumulation, and the outputs of the coherent accumulation andnon-coherent accumulation are taken as a extracted basis of thecharacteristic parameters.

In the second step, pick up the strongest path Max_Path; the Max_Path isthe path with maximum power amplitude (power strength) in the wholepower delay profile.

In the third step, evaluate the Average_Noise_Power, theTime_Of_First_Path_Arrival and the Time_Of_Max_Path_Arrival. With thepresent mature technique, the Average_Noise_Power is evaluated in twosteps: first, take N (N=5, for example) strongest paths away from thepower delay profile, second, make average within the searching windowfor the power delay profile in which N paths have been taken away;wherein way to take a strongest path away is as follow: select thestrongest path on the power delay profile, set values of samples in therange that covers three sample points at both side of the strongest pathsample to zero, thereby one path power of the power delay profile havingbeen taken away, which will be used for taking away the strongest pathnext time, is obtained; repeat N−1 times of the above procedure toobtain the power delay profile in which the N strongest paths have beentaken away (when the number of paths is less than N, some noise powerswill be taken away, which does not affect application).

In the fourth step, determine the Local_Max_Path that must be selectedat the range that has Alpha (α) microsecond delay from the Max_Path; ifthere is no detectable path in said range, take Theta (θ) (such as 2)multiple of noise average power as the Local_Max_Path value. The purposeto take said range that has Alpha (α) microsecond delay from theMax_Path is to avoid the strong reflect path that follows the Max_Pathin a LOS channel; the Alpha (α) should be taken more than one chipwidth.

In the fifth step, make detection according to the following twoformulas:Max_Path/Local_Max_Path>K  (1)Time_Of_First_Path_Arrival−Time_Of_Max_Path_Arrival<T  (2)

Formula (1) detects whether a ratio of the strongest path and the localstrongest path (Max_Path/Local_Max_Path) is greater than a threshold K.For the Local_Max_Path, there are two possible situations: there is alocal strongest path or there is not a local strongest path; in thelater situation, Theta (θ) multiple of the noise average power (θ=2) istaken as its value. For indoor and outdoor environment, the threshold Kis different; usually the indoor threshold is less than the outdoorthreshold, and here K is taken 10 as the outdoor threshold.

Formula (2) detects whether the arriving time difference between thefirst path and the maximum path is less than a setting value T; T iswithin three chips time and typically it is taken two chips time.

In the sixth step, if formulas (1) and (2) are satisfied simultaneously,determine that it is a LOS channel; if they are not satisfiedsimultaneously, determine that it is a NLOS channel.

In real, the power delay profile is various; in some specificenvironments, the Max_Path/Local_Max_Path of the LOS channel may overlapthe Max_Path/Local_Max_Path of the NLOS channel. For differentiation, inthis situation the threshold K is divided into two values K1 and K2,wherein K1>K2, for example K1 is taken 10 and K2 is taken 5.

When (Max_Path/Local_Max_Path)>K1, it is a LOS channel; when(Max_Path/Local_Max_Path)<K2, it is a NLOS channel; and whenK1>(Max_Path/Local_Max_Path)>K2, it is an undetermined channel.

FIG. 4 shows a flowchart for identifying a NLOS channel by using powerdifference between paths and {overscore (τ)}/σ. The flowchart is dividedinto two parts; the first part uses power difference between paths toidentify the LOS channels, i.e., the first part makes detection by meansof amplitude difference between a direct path and a non-direct path;then the second part further identifies the NLOS channels having beenidentified by the first part to determine the LOS channel or the NLOSchannel.

The first step and second step detect whether the channel is a LOSchannel or a NLOS channel by using amplitude difference; this is same asthe procedure described in FIG. 3.

During selection of the threshold K, it is kept in mind that greatmissing detection probability is taken to ensure that less falsedetection probability. The missing detection means that parts of LOSchannels are missed detecting into NLOS channels, and the falsedetection means that NLOS channels are detected into LOS channelsfalsely. Thereby the result is that there are some power delay profilesof LOS channel not fulfilling formula (1), and these LOS channels shouldbe further detected by the {overscore (τ)}/σ difference of the powerdelay profile between a LOS channel and a NLOS channel. This is what thethird step to seventh step will be done in FIG. 4.

Third step computes the delay of each path (detectable i^(th) path) tothe first detectable path (the First Path) with formula (3), i.e.computing the arrival time difference τ_(i) between the i^(th) path andthe First Path.τ_(i)=Time_Of_ith_Path_Arrival−Time_Of_First_Path_Arrival  (3)

Fourth step computes the mean delay {overscore (τ)} and the delay spreadσ. Theoretically, the mean delay {overscore (τ)} and the delay spread σare defined as followings:

$\begin{matrix}{\overset{\_}{\tau} = \frac{\sum\limits_{i = 1}^{n}{\tau_{i}*p_{i}}}{\sum\limits_{i = 1}^{n}p_{i}}} & (4) \\{{\overset{\_}{\tau}}^{2} = \frac{\sum\limits_{i = 1}^{n}{\left( \tau_{i} \right)^{2}*p_{i}}}{\sum\limits_{i = 1}^{n}p_{i}}} & (5) \\{\;{{\sigma = \sqrt{{\overset{\_}{\tau}}^{2} - \left( \overset{\_}{\tau} \right)^{2}}};}} & (6)\end{matrix}$

Wherein n is the number of detectable paths, τ_(i) is the delay of thei^(th) path to arrival time of the LOS path (if it exists), and p_(i) isthe power of the i^(th) path.

In real, general speaking, it is impossible to measure a LOS patharrival time defined in the formulas. In order to compute {overscore(τ)}, the invention takes the real measured time of the First Patharrival time (Time_Of_First_Path_Arrival−Time) as a starting point, andthe obtained {overscore (τ)} is less than the theoretical mean delayobtained by taking a delay to which the direct distance between the basestation and mobile station corresponds as the starting point, but in aLOS environment this decrement is very little. Nevertheless, in a NLOSenvironment there is a larger difference between the {overscore (τ)}computed from formula (3) and the real {overscore (τ)}; this can be seenby comparing FIG. 2 a and FIG. 2 b.

Since σ is kept unchanged, in the NLOS environment the computed{overscore (τ)}/σ value is obviously less than the real value, but inthe LOS environment the computed {overscore (τ)}/σ value is notobviously less than the real value; the result is that the difference of{overscore (τ)}/σ value between the LOS environment and the NLOSenvironment is decreased, and this will decrease the identificationaccuracy.

Fifth step computes {overscore (τ)}/σ value with formula (7) anddetermines what kind of the channel is according to an area where thecomputed {overscore (τ)}/σ value located.Gama={overscore (τ)}/σ  (7)

Sixth step compares the Gama and Delta with formula (8) to identify aNLOS channel.Gama={overscore (τ)}/σ<Delta (Δ)  (8)

Seventh step may take Delta (Δ)=0.6 (Delta may take a value between 0.5to 1), and determines a LOS channel for those that the {overscore (τ)}/σare less than 0.6 and a NLOS channel for those that the {overscore(τ)}/σ are not less than 0.6.

FIG. 5 is an embodiment of the invention. In FIG. 5, the LOSidentification module in the base station (NodeB) identifies whether achannel is a LOS channel or a NLOS channel for a result of de-spread,coherently and de-coherently accumulated; the identified result is sentup, through interface Iub, to the location estimation unit in the RadioNetwork Controller (RNC), which is called base station controller inGSM; the location estimation unit will use the identified result toimprove the location estimation accuracy.

Besides implementing the LOS identification in the NodeB, the LOSidentification module may be put in the User Equipment and theidentified result is sent to the NodeB and RNC through the Uu interface.

The method for identifying a LOS channel and a NLOS channel in theinvention may also be used to identify a channel in high speed datatransmission.

1. A method for identifying whether a channel is a LOS channel or a NLOSchannel in a mobile communication system, comprising: A. reading in apower delay profile; B. selecting a path with maximum power amplitude,i.e. a Maximum Path, from the power delay profile; C. estimating anaverage noise power and arrival time of a First Path and the MaximumPath; D. detecting a Local Maximum Path value within a searching window,and detecting whether a power ratio of the Maximum Path to the LocalMaximum Path is greater than a threshold K; E. detecting whether thearrival time difference between the First Path and the Maximum Path isless than a time interval T; F. if the power ratio of the Maximum Pathto the Local Maximum Path is greater than the threshold K, andsimultaneously the arrival time difference between the First Path andthe Maximum Path is less than the time interval T, determining thechannel being a LOS channel; otherwise determining the channel being aNLOS channel.
 2. The method according to claim 1, after the step F,further comprises a step of detecting whether the NLOS channeldetermined by Step F is a LOS channel or a NLOS channel, by {overscore(τ)}/σ difference of the power delay profile between the LOS channel andthe NLOS channel, which comprises: G. computing τ_(i) that is an arrivaltime difference between a i^(th) detectable path and first detectablepath; H. according to following formulas, computing mean delay{overscore (τ)} and root-mean-square delay spread σ of each detectablepath,${\overset{\_}{\tau} = {{\frac{\sum\limits_{i = 1}^{n}{\tau_{i}*p_{i}}}{\sum\limits_{i = 1}^{n}p_{i}}\mspace{31mu}{\overset{\_}{\tau}}^{2}} = {{\frac{\sum\limits_{i = 1}^{n}{\left( \tau_{i} \right)^{2}*p_{i}}}{\sum\limits_{i = 1}^{n}p_{i}}\mspace{31mu}\sigma} = \sqrt{{\overset{\_}{\tau}}^{2} - \left( \overset{\_}{\tau} \right)^{2}}}}};$I. computing {overscore (τ)}/σ that is a ratio of mean delay toroot-mean-square delay spread of power delay profile; if {overscore(τ)}/σ is less than Delta(Δ), determining the channel being a LOSchannel, and if {overscore (τ)}/σ is not less than Delta (Δ),determining the channel being a NLOS channel; wherein {overscore (τ)} isthe mean delay of a power delay profile and σ is a root-mean-squaredelay spread of the power delay profile; wherein n is number ofdetectable paths, p_(i) is the i^(th) path power, and i is 1 to n. 3.The method according to claim 2, wherein Step I comprises taking theDelta between 0.5 to
 1. 4. The method according to claim 1, wherein theStep D further comprises, if there is no detectable path in thesearching window of the Local Maximum Path, taking Theta (θ) multiplesof the average noise power as the Local Maximum Path power.
 5. Themethod according to claim 4, the Theta (θ) is taken
 2. 6. The methodaccording to claim 1, wherein Step D comprises, selecting the said LocalMaximum Path from a range within Alpha (α) microsecond that delays theMaximum Path; wherein the Alpha (α) width is greater than one chip. 7.The method according to claim 1, wherein Step D comprises, setting thethreshold K in indoor environment less than the threshold in outdoorenvironment, and setting the threshold in outdoor environment being 10.8. The method according to claim 1, wherein Step D further comprises,dividing the threshold K into K1 and K2, wherein K1>K2; wherein Step Ffurther comprises, if the power ratio of the Maximum Path to the LocalMaximum Path is greater than K1, determining the channel as a LOSchannel; if the ratio is less than K2, determining that the channel is aNLOS channel; and if said ratio is between K1 and K2, determining thatthe channel is an undetermined channel.
 9. The method according to claim8, the threshold K1 is taken 10 and K2 is taken
 5. 10. The methodaccording to claim 1, wherein Step E comprises, taking the time intervalT being within three chips, and typically two chips.
 11. The methodaccording to claim 2, wherein the Step D further comprises, if there isno detectable path in the searching window of the Local Maximum Path,taking Theta (θ) multiples of the average noise power as the LocalMaximum Path power.
 12. The method according to claim 2, wherein Step Dcomprises, selecting the said Local Maximum Path from a range withinAlpha (α) microsecond that delays the Maximum Path; wherein the Alpha(α) width is greater than one chip.
 13. The method according to claim 2,wherein Step D comprises, setting the threshold K in indoor environmentless than the threshold in outdoor environment, and setting thethreshold in outdoor environment being
 10. 14. The method according toclaim 2, wherein Step D further comprises, dividing the threshold K intoK1 and K2, wherein K1>K2; wherein Step F further comprises, if the powerratio of the Maximum Path to the Local Maximum Path is greater than K1,determining the channel as a LOS channel; if the ratio is less than K2,determining that the channel is a NLOS channel; and if said ratio isbetween K1 and K2, determining that the channel is an undeterminedchannel.
 15. The method according to claim 2, wherein Step E comprises,taking the time interval T being within three chips, and typically twochips.